Ultrafast exciton dynamics in semiconducting single-walled carbon nanotubes

To define the origin of the electronic excited states of single-walled carbon nanotubes, femtosecond fluorescence up-conversion and frequency-resolved transient absorption measurements were used for selective excitation/probing of particular nanotubes in a micelle-dispersed preparation enriched with individual nanotubes. Analysis of the temporal and intensity profiles of the transient signals enable one to unambiguously identify the excitonic nature of elementary excitations in semiconducting nanotubes, and the predominant dynamical process as a remarkable manifestation of exciton-exciton annihilation. These studies convincingly support the conclusion that the longest wavelength electronic excitations are of excitonic origin. In addition, evidence is shown for bi-exciton formation in single walled nanotubes.